Hydrogen purification and storage system

ABSTRACT

A method of purifying and storing hydrogen or otherwise separating hydrogen gas from a gaseous mixture containing hydrogen is disclosed. A mixture of hydrogen and other gaseous components is applied under pressure to a hydride container holding a hydride forming material adapted to adsorb at least hydrogen from the gaseous mixture. Cooling of the hydride forming material facilitates adsorption of hydrogen and other gases from the gas mixture. By selectively heating the hydride forming material, following the adsorption step, hydrogen and the other adsorbed gases are selectively released and can, thus, be separated from each other. If hydrogen is the only gaseous component of the gas mixture which is adsorbed during the adsorption step, then substantially pure hydrogen is obtained by heating the hydrogen-loaded hydride material sufficiently to release the purified hydrogen therefrom.

This is a division, of application Ser. No. 682,836 filed May 4, 1976,now U.S. Pat. No. 4,108,605.

BACKGROUND OF THE INVENTION

This invention relates to a system for purifying hydrogen and inparticular to such a system in which hydride forming material isutilized to purify hydrogen.

Because of the abundance of hydrogen and its relatively pollution-freeburning qualities, the desirability of developing hydrogen as an energysource has long been recognized. Perhaps the principal drawback inutilizing hydrogen thus far has been the difficulty of efficiently andsafely storing hydrogen. Storing hydrogen as a liquid is costly, sinceit requires considerable energy to liquify the hydrogen, and transfer ofthe liquid from one container to another results in a loss to theatmosphere of much of the hydrogen. Also, containers for liquid hydrogenmust be extremely well insulated to reduce loss of hydrogen due tovaporization or boiling. Storing hydrogen as a gas requires extremelyheavy and bulky containers and is impractical for most presentlycontemplated uses.

The use of hydride forming material (hereinafter defined to mean anymetals, metal compounds or alloys or other materials capable ofadsorbing and holding hydrogen) appears to be an attractive approach tothe storage of hydrogen. Exemplary hydride forming material includesiron titanium, misch-metal tetranickel and columbium. Storage ofhydrogen in the hydride forming material (to form hydrides by what issometimes referred to as hydriding) typically involves applying hydrogengas under pressure to the material and then dissipating the heatgenerated by the hydriding process. After the material adsorbs thehydrogen, the material is sealed in a container under pressure tomaintain the material in the "hydrided" state until the hydrogen isneeded at a subsequent time. Recovery or withdrawal of the hydrogeninvolves a process substantially opposite that used for storing thehydrogen, i.e., releasing some of the pressure of the container in whichthe hydride is maintained.

Hydride forming material presently contemplated for use in storinghydrogen not only adsorbs hydrogen but also some impurity gases, such aswater vapor and oxygen, which are generally present with commercialsources of hydrogen. Some impurity gases are more readily released fromthe hydride forming material than is hydrogen and some are less readilyreleased. If hydride forming material is repeatedly "charged" withhydrogen and the latter type impurities and then only the hydrogen isreleased for use, ultimately the hydride forming material will haveadsorbed so much impurity gas that it becomes unsuitable for storinghydrogen. Thus, the simple process of repeatedly applying such impurehydrogen to hydride forming material for storage is undesirable sincethe material eventually becomes incapable of the desired adsorption ofhydrogen.

Another problem of storing hydrogen in hydride forming material arisesfrom the fact that most such material is granulated so that a certainamount of void space is present in the material. This can beadvantageous in one respect since it facilitates the flow of hydrogenthrough the material during the hydriding process, but disadvantageousin anothr respect since the voids receive and retain the impuritiespresent with the hydrogen which are not adsorbed. Of course, it would bedesirable to purge the impurities from the voids prior to supplying thehydrides to users since the presence of such impurities might bedetrimental to the intended use.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simple,inexpensive and efficient system for purifying and storing hydrogen.

It is also an object of the present invention to provide such a systemwherein little hydrogen is wasted during the process of storing thehydrogen.

It is a further object of the present invention, in accordance with oneaspect thereof, to provide such a system which utilizes hydride formingmaterial to purify the hydrogen and wherein the hydride forming materialmay be repeatedly used with little diminishment of its hydrogenadsorbing abilities.

The above and other objects of the present invention are realized in anillustrative hydrogen purification system in which a mixture of hydrogenand impurities is applied to a container holding hydride formingmaterial capable of adsorbing hydrogen and impurities, of releasinghydrogen at one temperature and pressure, and of releasing theimpurities at another temperature and pressure. After hydrogen andimpurities are adsorbed by the hydride forming material in thecontainer, the temperature and pressure in the container are controlledto enable release of the hydrogen from the material but to preventrelease of at least certain of the impurities. The released hydrogen isthen delivered to a utilization unit (second container, hydrogen fueledengine, etc.). The hydrogen delivered to the utilization unit issubstantially purged of certain unwanted impurities.

This purification and delivery process may be continued until thehydride material in the container reaches a point where it has adsorbedso much impurity gas as to lower its hydrogen adsorbing capability bysome predetermined amount. When this point is reached, either thehydride container may be discarded or the temperature and pressure inthe hydride container controlled so that at least certain of theimpurities are released from the hydride material and from thecontainer. In the latter case, the container would then be ready to onceagain perform its impurity purging function. In this manner, impuritieswhich tend to be adsorbed by hydride material but which are not readilyreleased under the same conditions as is hydrogen are first removed fromthe hydrogen/impurity mixture so that relatively impurity free hydrogenmay be passed to and used by another unit.

In accordance with one aspect of the invention, a second containerholding hydride forming material is attached to the first mentionedcontainer to receive hydrogen released from the first container. Afterthe second container has been "charged" with hydrogen, some of theadsorbed hydrogen is released to purge from the voids in the hydrideforming material impurities which may not have been removed in the firstcontainer nor adsorbed in the second container. The second containerthus contains reasonably pure hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from a consideration of the followingdetailed description presented in connection with the accompanyingdrawings in which:

FIG. 1 is a diagram of one illustrative embodiment of a hydrogenpurification system made in accordance with the principles of thepresent invention; and

FIG. 2 is a diagram of another illustrative embodiment of a hydrogenpurification system also made in accordance with the principles of thepresent invention.

DETAILED DESCRIPTION

In a simple embodiment of the present invention, a hydride bed orcontainer 4 (FIG. 1) is coupled in series between an impure hydrogensource 16 and a hydrogen utilization unit 12. Obviously, the hydrogensource 16 is not purposefully made impure, but practically it isdifficult to obtain hydrogen which does not contain impurities. Thehydrogen utilization unit 12 might illustratively be another hydridecontainer, a hydrogen burning engine, etc. A mixture of hydrogen andimpurity gases is delivered by the source 16 to the hydride container 4where the more reactive impurities are adsorbed by the hydride formingmaterial in the container. The partially purified mixture is thenconveyed to the utilization unit for either storage or direct use.Exemplary impurities which could be removed from the mixture by simplypassing the mixture through the container 4 include chlorine gas andfluorine gas.

For these particular impurities and other highly reactive impurities, itmay be impractical to attempt to recover and reuse the hydride formingmaterial by driving off the impurities from the material. In such acase, the hydride container 4 (or just the hydride forming materialtherein) would be thrown away after the hydride forming material hadadsorbed some predetermined amount of impurities, i.e., when thematerial became so saturated with impurities that it could no longerreadily function to adsorb additional impurities.

A more complicated embodiment of the present invention will now bedescribed in connection with FIG. 1. This embodiment is for use inremoving impurities which, although less readily released from hydrideforming material (once adsorbed) than is hydrogen, nevertheless may bereleased from the material by taking appropriate measures such asheating the material. In this embodiment, a second hydride container 8is coupled in parallel with the hydride container 4. The impure hydrogensource 16 is coupled by way of a control valve 20 to the hydridecontainers 4 and 8 and the hydride containers, in turn, are coupled tothe hydrogen utilization unit 12 by way of a control valve 24. Thecontrol valve 20 operates to direct hydrogen and impurities from thesource 16 either to the hydride container 4, the hydride container 8 orto both, and the control valve 24 operates to direct hydrogen fromeither the container 4 or the container 8 to the utilization unit 12 orfrom both containers 4 and 8 to the unit 12. Such bi-directional valvesare well known in the art.

Both hydride containers 4 and 8 include outlets 28 and 32 and outletvalves 36 and 40 respectively. These outlets and valves simply controlthe release of gases from the hydride containers into the atmosphere.These outlets and valves are provided so that impurity gases adsorbed bythe hydride material in the containers 4 and 8 can, from time to time,be driven off as will be explained shortly. This allows use and reuse ofthe containers 4 and 8 and the hydride forming material therein.

To facilitate both adsorption and release of hydrogen and impuritiesfrom the hydride forming material in the hydride containers 4 and 8, acooling fluid pump and heat exchanger 44 and a heating fluid pump andheat exchanger 66 are provided. The heat exchanger 44 supplies coolingfluid to coil conduits 48 disposed in the containers 4 and 8 (shown bydotted line only in container 8 of the drawing). The cooling fluid issupplied by the pump and heat exchanger 44 to a conduit 52 and thendirected by control valves 56 and 58 to the coil conduits in eithercontainer 4, container 8, or both. The cooling fluid flows through thecontainer conduits 48 through control valves 60 or 62 back to the pumpand heat exchanger 44. In a similar manner, heating fluid from the pumpand heat exchanger 66 is conveyed via control valves 70 and 72 either tocontainer 4, or container 3, or both, and from the hydride containersvia control valves 74 and 76 back to the pump and heat exchanger 66.Thus, both cooling fluid and heating fluid may be conveyed intoproximity with the hydride forming material held in the containers.Although a very simple hydride container is shown in the drawing, itshould be understood that any one of a variety of different type hydridecontainers could be devised and arranged generally in the arrangementshown in the drawing. Exemplary hydride containers are disclosed incopending application, Ser. No. 570,268.

The cooling fluid from the pump and heat exchangers 44 is used tofacilitate adsorption of both hydrogen and impurities by the hydrideforming material held in the containers 4 and 8, and the heating fluidfrom the exchanger 66 is used to facilitate release of either hydrogenor the impurities. The cooling fluid is applied by the pump and heatexchanger 44 to the container conduits 48 to adsorb and carry away heatproduced by the hydride forming material during the adsorption process.The heating fluid is applied by the pump and heat exchanger 66 to thecontainer conduits 48 to heat the hydride forming material to varioustemperatures to thereby induce release of either the hydrogen or theimpurities held by the material. This will become very clear withfurther description of the operation of the system.

Impure hydrogen from the source 16 is applied under pressure via thecontrol valve 20 to the hydride container 4. As indicated earlier, thehydrogen source 16 is not purposefully made impure but practically, itis difficult to secure hydrogen which does not include some"impurities." As the mixture of hydrogen and impurities is applied tothe hydride container 4, cooling fluid is circulated through conduits inthe container by the pump and heat exchanger 44 to facilitate adsorptionof the hydrogen and impurities by the hydride forming material in thecontainer. The rate at which the hydrogen and impurities are adsorbed isdependent upon both the pressure under which the mixture is applied tothe container and the temperature of the hydride forming material. Thelower the temperature and greater the pressure, the faster is the rateof adsorption and the greater is the amount which would be adsorbed.While the mixture is being applied to the hydride container, controlvalve 24 is closed as is outlet control valve 36.

After the hydride forming material in the container 4 has adsorbedhydrogen and impurities, the control valve 20 is operated to directmixture from the source 16 to the hydride container 8. Control valve 58is operated to prevent further supply of the cooling fluid to thehydride container 4, control valve 56 is opened to allow cooling fluidto flow to the conduit 48 of the container 8, control valve 70 isclosed, and control valve 72 is opened to allow flow of heating fluid tothe conduit in the hydride container 4. Control valves 60, 62, 74 and 76are similarly operated to direct heating fluid from the hydridecontainer 4 back to the heating fluid pump and heat exchanger 66 and todirect cooling fluid from the hydride container 8 back to the coolingfluid pump and heat exchanger 44. With cooling fluid flowing to thecontainer 8, the hydride forming material held therein adsorbs hydrogenand impurities from the mixture supplied by the source 16. With heatingfluid being supplied to the hydride container 4, the hydride formingmaterial is induced to release hydrogen which flows through controlvalve 24 to the utilization unit 12. The temperature of the heatingfluid from the heat exchanger 66 is maintained at a level justsufficient to induce the release of hydrogen, but not those impuritieswhich are less readily released than is hydrogen. Thus, principally onlyhydrogen is allowed to flow from the container 4 into the utilizationunit 12.

When the hydrogen previously adsorbed by the hydride material in thecontainer 4 has been transported to the utilization unit 12, and whenthe hydride forming material in the container 8 has adsorbed hydrogenand impurities, the control valves are operated so that mixture from thesource 16 is again directed to the container 4, so that cooling fluid isdirected to the conduit 48 in the container 4, and so that heating fluidis directed to the conduit 48 in the container 8. The hydride formingmaterial in the container 4 thus again is induced to adsorb hydrogen andimpurities and the hydride forming material in the container 8 isinduced to release principally only hydrogen for transfer to theutilization unit 12.

If the utilization unit 12 were a hydride container, then when thecontainer was sufficiently charged with substantially pure hydrogen, itwould be removed from the system and a new hydride container would beattached in its place. In this fashion, substantially pure hydrogen canbe supplied to and stored in hydride containers for later use.

After the hydride forming material in the hydride containers 4 and 8successively adsorbs hydrogen and impurities and releases hydrogen, theimpurities in the material will, of course, build up and thus reduce thecapability of the material to adsorb more impurities or hydrogen. Whenthe hydride forming material has adsorbed some predetermined quantity ofimpurity gases, heating fluid is supplied by the pump and heat exchanger66 to the containers at a temperature considerably higher than thetemperature maintained for inducing release of only the hydrogen and atthis latter temperature, the hydride forming material is induced torelease the impurities previously adsorbed. During this process, valves36 and 40 are opened to release the impurities into the atmosphere orsuitable waste sink (not shown). By heating the hydride forming materialto a sufficiently high temperature, the material in the containers ispurged of the impurities and may again be used for adsorbing hydrogenand impurities and for releasing hydrogen as previously described.

The temperatures and pressures at which impurities and hydrogen would beadsorbed and released from the hydride forming material depends upon theimpurities of interest and the hydride forming materials used. Thesetemperatures and pressures can be readily determined by experiment. Ithas been found, for example, that iron titanium adsorbs and releaseshydrogen at room temperature (about 72° F.) and so much adsorption andrelease can be controlled by controlling the pressure in the hydridecontainers--increase in pressure induces adsorption of hydrogen anddecrease in pressure induces release of hydrogen. To release impurities,the temperature of the iron titanium is simply increased until theimpurities are driven off.

It should be understood that certain impurities may be adsorbed andreleased by hydride forming material under substantially the samecircumstances as with hydrogen. Such impurities are not of concern inthe present invention since the concern is removal of impurities whichare not readily released from hydride material but rather which build upin the hydride material to hamper or inhibit adsorption of hydrogen(embodiment of FIG. 1) and impurities which are not as readily adsorbedas is hydrogen (embodiment of FIG. 2 to be discussed momentarily). Byemploying the system and method of FIG. 1, certain undesirableimpurities are first removed from the hydrogen before it is applied tothe utilization unit 12 so that the utilization unit is not adverselyaffected by the impurities.

The embodiment of the present invention shown in FIG. 2 is designed toremove impurities which are less readily adsorbed than is hydrogen. Asshown in FIG. 2, hydride containers 102 are coupled in a series orcascaded relationship which, as will become clear as the descriptioncontinues, facilitates purification and storage of hydrogen with verylittle loss of hydrogen.

A source of impure hydrogen gas 106 is coupled via a control valve 110into one end of the first hydride container 102 of the series ofcontainers. The other end of the first container is coupled by way of acontrol valve 114 and a check valve 1l8 into one end of the secondcontainer of the series and so on. The last hydride container in theseries is coupled by way of a control valve 122 to a waste sink 126.With this arrangement, hydrogen plus whatever impurities are presentflow from the source 106 through the first hydride container in theseries and then successively through the remaining containers to thesink 126.

To facilitate adsorption of hydrogen by the hydride material held in thecontainers 102, a source of cooling fluid is provided to adsorb andcarry away heat produced by the hydride material during the hydridingprocess. Thus, a cooling fluid pump and heat exchanger 130 is coupled tothe first and last container in the series to coil conduits 134 (shownby dotted line in FIG. 1) disposed in the containers. Each of the coilconduits 134 is also coupled by way of connecting conduits 138 tosimilar coil conduits in adjacent containers. In this manner, coolingfluid is conveyed into proximity with the hydride material held in thecontainers.

Impure hydrogen from the source 106 is applied under pressure via thecontrol valve 110 to the first hydride container 102 of the series. Themixture of hydrogen and impurities flow through the first containerduring which time some of the hydrogen is adsorbed by the hydrideforming material in the container, and then through control valve 114and check valve 118 into the second container in the series. (This, ofcourse, assumes that the impurities in question here are not as readilyadsorbed as is hydrogen. Examples of such impurities are nitrogen andargon.) Because some of the hydrogen of the mixture was adsorbed in thefirst container, the mixture flowing from the first container to thesecond container will have a higher concentration of impurities than themixture applied to the first container. Still more hydrogen is adsorbedin the second container and thus additionally diluted mixture is passedto the third container in the series, etc.

To maintain the flow of mixture from the source 106 to the sink 126, thecontrol valves 110, 114, . . . and 122 are operated to control the flowof mixture therethrough and maintain the pressure of the mixture in thefirst container higher than the pressure in the second container which,in turn, is maintained higher than the pressure in the third container,etc. Of course, the control valves 110 through 122 are proportionalvalves to provide variable flow of the mixture from one container to thenext. Maintaining the pressure in this fashion not only facilitates theflow of the mixture through the series of containers but also enhancesthe speed at which hydrogen is adsorbed by the hydride forming materialin the containers. The check valves 118 in the conduits connecting thecontainers prevent the backflow of mixture.

The cooling fluid is pumped from the unit 130 to the hydride containersand through the coil conduits 134. As the cooling fluid passes throughthe hydride containers, it adsorbs heat produced during the hydridingprocess.

When the hydride forming material in the first container has adsorbed acertain amount of hydrogen, the control valve 110 is closed to preventfurther application of mixture to the container. At this point, mixture(including hydrogen and impurities) would remain in the voids among thegranular hydride forming material. To eliminate the impurities from thefirst container, the hydride forming material in the container isinduced to release some of the hydrogen and the control valve 114 isoperated to allow the released hydrogen to force the mixture from thefirst container to the second container in the series. The amount ofhydrogen so released would depend upon the void space volume but, in anycase, it would generally be only a small percentage of the total amountof hydrogen adsorbed and held in the hydride forming material. This isso since most hydride forming material adsorbs many times its volume inhydrogen.

After the impurities are purged from the first container in the series,either the container itself could be removed from the series arrangementor the hydrogen in the container could be removed depending upon the useto which the hydrogen was to be put. If the containers were removed,advantageously a new container would be inserted at the end of theseries between what was initially the last container in the series andthe sink 126. The source 106 would then be connected to what initiallywas the second container in the series, and the purification processwould be continued.

Because hydrogen is adsorbed by the hydride forming material in eachcontainer as the mixture of hydrogen and impurities passes from thesource 106 through each of the containers in series, the mixtureultimately passing into the sink 126 contains mostly impurities and verylittle hydrogen. Thus, the mixture applied to the sink 126 could simplybe vented or discharged and very little loss of hydrogen would result.The system and method described in FIG. 2 thus provides for obtainingsubstantially pure hydrogen with very little resultant hydrogen loss.

Although three different embodiments of the present invention have beendescribed separately, it should be understood that any combination ofthe embodiments could be provided to cooperate in removing the variousimpurities. For example, the system of FIG. 2 could be coupled in seriesdownstream of the system of FIG. 1. That is, the input to the firsthydride container 102 in the series of FIG. 2 could be coupled to theoutput of valve 24 of FIG. 1. With this arrangement, the FIG. 1 portionof the combination would serve to remove the more highly reactiveimpurities and the FIG. 2 portion would serve to remove impurities whichare less readily adsorbed than is hydrogen.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements.

What is claimed is:
 1. A method of separating a hydrogen enriched gasfrom a gas mixture containing hydrogen and other gaseous components,comprising(a) supplying said gas mixture to a hydride container having ahydride forming material therein which is adapted to adsorb hydrogen gasfrom said gas mixture, (b) venting unadsorbed gaseous components of saidgas mixture from said hydride container, (c) treating thehydrogen-loaded hydride material in said hydride container to desorb andrelease a hydrogen enriched gas therefrom, by controlling thetemperature of said hydride forming material and the pressure in saidhydride container so that hydrogen is released from said hydride formingmaterial with substantially none of the other gaseous components whichmay have been adsorbed by said hydride forming material being released,(d) delivering the hydrogen enriched gas from said hydride container toa hydrogen utilization unit, (e) heating said hydride forming materialto a second temperature greater than the controlled temperature of step(c) while maintaining the pressure in said hydride container at least nogreater than the controlled pressure of step (c) to cause other gaseouscomponents which may have been adsorbed by said hydride forming materialto be released therefrom, and (f) releasing said other gaseouscomponents from said hydride container.
 2. A method in accordance withclaim 1, wherein step (a) further comprises controlling the temperatureof said hydride forming material by cooling said material to remove heatgenerated when hydrogen and any other gaseous components are adsorbed bysaid material.